Processes are known for making stretchable stitch-bonded nonwoven fabrics by multi-needle stitching of a fibrous layer with elastic yarn. Earlier patents disclosing such processes include U.S. Pat. No. 4,704,321, which describes stitching and contracting non-bonded plexifilamentary polyethylene sheets, U.S. Pat. No. 4,876,128, which discloses stitching and contracting bonded fibrous layers, and U.S. Pat. No. 4,773,238, which describes stitching a substantially non-bonded web and then contracting the stitched fabric to less than half its original area, among others.
To produce a highly stretchable stitch-bonded fabric by these known processes generally required that the stitched fabric be allowed to contract or gather extensively after the stitching step. The contraction was caused by the retractive power of the elastic stitching yarns. Stitch-bonding with elastic yarns usually was not performed with accurately controlled tensions on (a) the fibrous substrates fed to the stitch-bonding machine, (b) on the elastic yarns fed to the stitching needles and/or (c) on the stitched fabrics leaving the machine. Generally, the stitch-bonding machines were operated with high tensions on each of these components. In addition, the elastic yarns were subjected to increased tension by the action of the stitching needles of the stitch-bonding machine. Accordingly, the yarns arrived at the stitching needles with high elongations and were inserted into the fibrous layer with very little residual stretch remaining in the yarns. The elongation of the stitched yarn usually was quite close to its break elongation.
For example, as described in the '238 patent, the elastic yarns were fed to the stitch-bonding machine with an elongation of 100 to 250%, and then further stretched by the action of the stitching needles. The high elongation and low residual stretch of the elastic yarns in the stitched fabric were evident from the large contraction of the stitch-bonded fabric as it exited the stitching machine, despite a high wind-up tension applied to the exiting fabric, and from the inability of the stitched and contracted fabrics to be stretched much beyond its original stitched dimensions. It was only after the contraction that the fabrics could be stretched significantly.
U.S. Pat. No. 4,998,421 discloses a process for making an elastic stitch-bonded fabric, which does not require large contraction of the fabric after stitching in order to achieve stretchability. The non-woven substrates described in the '421 patent include “substantially nonbonded” webs wherein “the fibers are not generally bonded to each other by chemical or thermal action”. To improve durability (e.g., wash resistance, surface stability and abrasion resistance), such substrates are needle-punched or point-bonded or line-bonded. While such actions improve the durability of the substrates, they also reduce the stretchability of the substrates.
U.S. Pat. No. 5,879,779 also discloses stitch-bonded fabrics utilizing “lightly bonded or unbonded nonwovens” stitched with stretchable “POY” yarns. The fabrics can be stretched to a limited degree beyond their original “as-stitched” dimensions making them “moldable.” They can also be shrunk, and then stretched. Only point bonded and entangled/spunlaced non-woven substrates are given as examples in the '779 patent. Extensive bonding of the fibers to each other, and extensive distribution of binder among the fibers and onto the surfaces of the fibers are avoided by using liquid chemical binders, sheath binders over high melting fiber cores and the like to prevent over bonding and the resulting loss of stretchability.
There remains a need in the art for stretchable stitch-bonded nonwoven fabrics that utilize the stretchability of the nonwoven substrate and do not require significant contraction of the fabrics after the stitch-bonding process before the fabrics achieve stretchability.